Optical filter including plates for filtering light and optical measuring device employing optical filter

ABSTRACT

Provided are an optical filter and an optical measuring device employing the optical filter. The optical filter comprises at least one pixel. The at least one pixel comprises a first reflective plate that is configured to receive the incident light and have a plurality of first holes formed therein; and a second reflective plate that is configured to transmit particular wavelength or range of wavelengths of the light transmitted through the first reflective plate, faces the first reflective plate with a gap between the first reflective plate and the second reflective plate, and has a plurality of second holes formed therein.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2014-0090354, filed on Jul. 17, 2014 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

Apparatuses and methods consistent with exemplary embodiments relate tooptical filters and optical measuring devices employing the same, andmore particularly, to optical filters designed to have a narrowlinewidth of light and change a wavelength being filtered during amanufacturing process and optical measuring devices employing theoptical filters, which are capable of measuring intensity of lightfiltered for each pixel.

2. Description of the Related Art

In general, optical spectrum analysis is used to measure and analyzephysical and chemical states of an object. This analysis technique isused in various industrial fields such as optics, medicine, chemistry,and ocean engineering.

In optical spectrum analysis, optical spectroscopy is used to splitlight into several wavelength ranges and measure intensity of the lightat each wavelength to analyze the spectrum of the light. The opticalspectroscopy is classified into a light scattering technique in whichincident light is transmitted through a periodic crystal structure andscattered in different directions at each wavelength and a filteringtechnique in which only light of a specific wavelength is transmittedthrough an optical filter.

In the light scattering technique, an optical sensor may be fixed, and acrystal structure may rotate so as to measure light of differentwavelengths that reach the optical sensor. Alternatively, a crystalstructure may be fixed, and a plurality of optical sensors may belocated at different positions so that each optical sensor measureslight of a particular wavelength.

In the filtering technique, an optical filter may be a metal meshfilter, a dichroic filter using a thin film, a filter using aFabry-Perot interferometer, or a pigment type color filter manufacturedby coating a substrate with a pigment-dispersed photoresist solution andpatterning the substrate.

In recent years, optical spectrum analysis has been used extensively ina variety of applications, beyond laboratory analysis, includingeveryday-life items such as portable and wearable devices. Thus, thereis an increasing need for a small-volume optical filter to filter a verynarrow linewidth wavelength region. Furthermore, as optical filters havebeen used in a wide variety of applications, a technique of easilychanging a wavelength being filtered by an optical filter during amanufacturing process has become an economically important issue.Furthermore, much attention is being directed toward miniaturization ofa device for measuring an optical spectrum by using an optical filter.

SUMMARY

Exemplary embodiments provide optical filters to filter a narrowlinewidth wavelength and change a wavelength being filtered by anoptical filter during a manufacturing process and optical measuringdevices employing the optical filters.

According to an aspect of an exemplary embodiment, there is provided anoptical filter comprising at least one pixel, wherein the at least onepixel may comprise: a first reflective plate that is configured toreceive the incident light have a plurality of first holes formedtherein; and a second reflective plate that is configured to transmitparticular wavelength or range of wavelengths of the light transmittedthrough the first reflective plate, faces the first reflective platewith a gap between the first reflective plate and the second reflectiveplate, and has a plurality of second holes formed therein.

The wavelength or range of wavelengths of light transmitted through thesecond reflective plate may correspond to a thickness of the first andsecond reflective plates.

The wavelength or range of wavelengths of light transmitted through thesecond reflective plate may correspond to a refractive index of amaterial of the first and second reflective plates.

The wavelength or range of wavelengths of light transmitted through thesecond reflective plate may correspond to a distance between the firstand second reflective plates.

The wavelength or range of wavelengths of light transmitted through thesecond reflective plate may correspond to sizes of the first and secondholes.

The wavelength or range of wavelengths of light transmitted through thesecond reflective plate may correspond to a spacing between adjacentones of the first holes or a spacing between adjacent ones of the secondholes.

The first and second holes may be arranged in regular patterns.

The first holes and the second holes may have a same shape andarrangement pattern.

The first holes may be vertically aligned to overlap with the secondholes.

The first and second holes may have a slit shape or circular shape.

The optical filter may comprise a plurality of pixels including the atleast one pixel, and wherein at least two of the pixels transmit lightof different wavelengths.

The optical filter may further comprise a lens configured to change apath of the light incident on the first reflective plate.

Each of the first and second reflective plate may comprise a materialhaving a refractive index greater than 3.

Each of the first and second reflective plates may comprise at least oneselected from a group consisting of gallium phosphide (GaP), mercurysulfide (HgS), gallium arsenide (GaAs), germanium (Ge), silicon (Si),silicon dioxide (SiO₂), silicon nitride (SiN), indium phosphide (InP),and any combinations thereof.

According to an aspect of another exemplary embodiment, there isprovided an optical measuring device comprising: an optical filtercomprising at least one first pixel; and a sensor that is configured tomeasure an intensity of light transmitted through the optical filter andincludes at least one second pixel corresponding to the at least onefirst pixel, wherein the at least one first pixel comprises: a firstreflective plate configured to receive the incident light and has aplurality of first holes formed therein; and a second reflective plateconfigured to transmit particular wavelength or range of wavelengths ofthe light transmitted through the first reflective plate, faces thefirst reflective plate with a gap between the first reflective plate andthe second reflective plate, and has a plurality of second holes formedtherein.

The wavelength or range of wavelengths of light transmitted through thesecond reflective plate may correspond to at least one selected from athickness of the first and second reflective plates, a refractive indexof a material of the first and second reflective plates, a distancebetween the first and second reflective plates, sizes of the first andsecond holes, a spacing between adjacent ones of the first holes, and aspacing between adjacent ones of the second holes.

The first and second holes may be arranged in regular patterns.

The first holes and the second holes may have a same shape andarrangement pattern.

The first and second holes may have a slit shape or circular shape.

The optical filter may further comprise a lens configured to change apath of the light incident on the first reflective plate.

Each of the first and second reflective plates may comprise a materialhaving a refractive index greater than 3.

Each of the first and second reflective plates may comprise at least oneselected from a group consisting of gallium phosphide (GaP), mercurysulfide (HgS), gallium arsenide (GaAs), germanium (Ge), silicon (Si),silicon dioxide (SiO₂), silicon nitride (SiN), indium phosphide (InP),and any combinations thereof.

The at least one second pixel may comprise an optical sensor configuredto measure an intensity of light transmitted through the at least onefirst pixel.

The optical measuring device may further comprise a correction processorconfigured to receive the intensity of light measured in the at leastone second pixel and correct the measured intensity of light inconsideration of transmittance of light transmitted through the at leastone first pixel.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become apparent and more readilyappreciated from the following description of exemplary embodiments,taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of an optical filter according to anexemplary embodiment;

FIG. 2 is an enlarged view of a pixel of FIG. 1;

FIG. 3 illustrates a simulation result of transmittance with respect toa wavelength of light passing through a pixel in the optical filter ofFIG. 1;

FIG. 4 illustrates a simulation result showing a change in a wavelengthto be filtered according to a distance between holes in the opticalfilter of FIG. 1;

FIG. 5 is a plan view of a plurality of first (or second) holes formedin a first (or second) reflective plate in the optical filter of FIG. 1;

FIG. 6 illustrates a cross-section of a pixel including the first andsecond reflective plates in the optical filter of FIG. 1;

FIG. 7 illustrates a modified example of a cross-section of the pixelshown in FIG. 6;

FIG. 8 illustrates a plurality of first (or second) holes formed in thefirst (or second) reflective plate in the optical filter of FIG. 1,according to another exemplary embodiment;

FIG. 9 illustrates a plurality of first (or second) holes formed in thefirst (or second) reflective plate in the optical filter of FIG. 1,according to another exemplary embodiment;

FIG. 10 is a perspective view of an optical filter according to anotherexemplary embodiment; and

FIG. 11 is an exploded perspective view of an optical measuring deviceincluding an optical filter, according to another exemplary embodiment.

DETAILED DESCRIPTION

Exemplary embodiments are described in greater detail below withreference to the accompanying drawings.

In the following description, like drawing reference numerals are usedfor like elements, even in different drawings. Sizes or thicknesses ofelements may be exaggerated for clarity. The matters defined in thedescription, such as detailed construction and elements, are provided toassist in a comprehensive understanding of the exemplary embodiments.However, it is apparent that the exemplary embodiments can be practicedwithout those specifically defined matters. Also, well-known functionsor constructions are not described in detail since they would obscurethe description with unnecessary detail. Expressions such as “at leastone of,” when preceding a list of elements, modify the entire list ofelements and do not modify the individual elements of the list.

FIG. 1 is a perspective view of an optical filter 10 according to anexemplary embodiment. The optical filter 10 according to the presentembodiment may be an optical device that selectively transmits only aparticular wavelength of incident light. The particular wavelength maybe set differently depending on the type of an optical device in whichthe optical filter 10 is disposed. For example, the optical filter 10may be an optical device for selectively transmitting light of differentwavelengths in the visible light, infrared light, and ultraviolet lightspectrum. However, this may be only an example, and exemplaryembodiments are not limited thereto.

As shown in FIG. 1, the optical filter 10 may include a plurality ofpixels including a pixel 100 or may include only the pixel 100.Accordingly, the pixel 100 may refer to all or a part of the opticalfilter 10 and may be the smallest unit region of the optical filter 10for filtering a specific wavelength or range of wavelengths of light.Thus, if the optical filter 10 includes only the pixel 100, the entireoptical filter 10 may be considered to be the pixel 100. On the otherhand, if the optical filter 10 includes the plurality of pixels forfiltering different wavelengths or ranges of wavelengths, each of theplurality of pixels, including the pixel 100, may filter itscorresponding wavelength or range of wavelengths among the differentwavelengths or ranges of wavelengths.

While FIG. 1 shows that the plurality of pixels in the optical filter 10are divided into rectangular parallelepipeds, exemplary embodiments arenot limited thereto. The pixel 100 may have any three-dimensional (3D)or two-dimensional (2D) shape according to the appearance or shape ofthe optical filter 10. Furthermore, although FIG. 1 shows that theplurality of pixels in the optical filter 10 have the same size,exemplary embodiments are not limited thereto, and the plurality ofpixels may have different volumes or sizes if necessary. At least two ofthe plurality of pixels may selectively transmit light of differentwavelengths. In other words, the plurality of pixels may filterdifferent wavelengths or ranges of wavelengths of light. However,exemplary embodiments are not limited thereto, and if necessary, any twoof the plurality of pixels may filter the same wavelength or range ofwavelengths.

FIG. 2 is an enlarged view of the pixel 100 of FIG. 1.

As shown in FIG. 2, the pixel 100 includes first and second reflectiveplates 110 and 120 that are separated from and oppose each other. Thefirst reflective plate 110 on which light is incident includes aplurality of first holes 112. The second reflective plate 120 is adaptedto receive light transmitted through the first reflective plate 110 andincludes a plurality of second holes 122. The plurality of the pixels inthe optical filter 10 of FIG. 1 may include the first and secondreflective plates 110 and 120 as shown in FIG. 2, but is not limitedthereto. For example, some of the plurality of pixels in the opticalfilter 10 of FIG. 1 may not include the first and second reflectiveplates 110 and 120. However, at least one of the plurality of pixels,for example the pixel 100, includes the first and second reflectiveplates 110 and 120.

The first and second reflective plates 110 and 120 may have any panelshape that reflects some of the incident light and transmits theremainder thereof. To selectively transmit some of the incident light,the first and second reflective plates 110 and 120 may include acomponent having a refractive index different from that of an externalmedium that is in contact with the first and second reflective plates110 and 120. Thus, when light incident from the external medium reachesthe first and second reflective plates 110 and 120, some of the incidentlight may be reflected, and the rest of the light may be transmitted. Asdescribed above, each of the first and second reflective plates 110 and120 may have a panel shape. The panel shape may refer to a shape havinga flat or curved surface and a thickness that is consistent or littlechange when measured from the surface of the first and second reflectiveplates 110 and 120. While FIG. 2 shows that the first and secondreflective plates 110 and 120 are rectangular in shape, exemplaryembodiments are not limited thereto. For example, the first and secondreflective plates 110 and 120 may have a circular, polygonal, or anyother shape.

As described above, the first and second reflective plates 110 and 120oppose each other and are separated from each other by a distance d asshown in FIG. 2. The distance d may be uniform, but may vary from onepixel 100 to another. “Opposing each other” may mean that first andsecond reflective plates 110 and 120 face each other as shown in FIG. 1.In other words, one of the first and second reflective plates 110 and120 may be parallel to the other or face the other with being slightlyoblique thereto.

The plurality of first holes 112 and the plurality of second holes 122are formed in the first and second reflective plates 110 and 120,respectively. In this case, the first and second “holes” 112 and 122 maybe regions penetrating the first and second reflective plates 110 and120, respectively. The first and second holes 112 and 122 may have thesame or different shapes. The first and second holes 112 and 122 mayalso have refractive indices close to or equal to that of an externalmedium. Due to formation of the first and second holes 112 and 122, thefirst and second reflective plates 110 and 120 may each have a highreflectance of light. In detail, reflectance on the surfaces of thefirst and second reflective plates 110 and 120 is higher than that onother reflective plates without the first and second holes 112 and 122,due to interference between light transmitted through the remainingregions of the first and second reflective plates 110 and 120 other thanthe first and second holes 112 and 122 and light transmitted through thefirst and second holes 112 and 122 as well as interference of lightwithin the first and second holes 112 and 122.

Due to the increase in reflectances of the first and second reflectiveplates 110 and 120, a linewidth of light of the optical filter may bedecreased. A linewidth of light may be a factor representing a range ofwavelengths of light being transmitted. Thus, as a linewidth of lightdecreases, only light of a narrow range of wavelengths may betransmitted. The linewidth of light may be determined according tovarious schemes. For example, the linewidth of light may be determinedby a difference between a wavelength at a peak of intensity in a graphof intensity against wavelength being passed through the optical filterand a wavelength corresponding to half the peak of intensity. This is anexample only, and a linewidth of light may be determined according toother various methods. A quality (Q) factor is a variable related to alinewidth of light of the optical filter and may be defined by Equation(1) below:

$\begin{matrix}{Q = \frac{\lambda_{c}}{\Delta\;\lambda}} & (1)\end{matrix}$where Δλ is a bandwidth in a graph of intensity of light againstwavelength being passed, and λ_(c) wavelength at the peak intensity.

Since a bandwidth (or linewidth) Δλ is decreased, a Q factor isincreased Thus, as the Q factor increases, a linewidth of light of theoptical filter 10 will decrease. The Q factor may be defined by Equation(2) below:

$\begin{matrix}{Q \propto \mspace{11mu}\frac{\left( {r_{1}r_{2}} \right)^{1/4}}{1 - \left( {r_{1}r_{2}} \right)^{1/2}}} & (2)\end{matrix}$where r₁ is a reflectance of the first reflective plate 110 and r₂ is areflectance of the second reflective plate 120.

As defined in Equation (2) above, with the increase in reflectances ofthe first and second reflective plates 110 and 120, the Q factorincreases, and thus a linewidth of light of the pixel 100 decreases.Thus, when the reflectances of the first and second reflective plates110 and 120 are increased due to formation of the first and second holes112 and 122 in the first and second reflective plates 110 and 120,respectively, a linewidth of light of the pixel 100 in the opticalfilter 10 may be decreased.

FIG. 3 illustrates a simulation result of transmittance with respect toa wavelength of light passing through the pixel 100 in the opticalfilter 10 of FIG. 1.

The simulation result of FIG. 3 is based on a simulation performed usingRigorous Coupled Wave Analysis (RCWA). In FIG. 3, the ordinate andabscissa represent a wavelength of incident light and a gap between thefirst and second reflective plates 110 and 120, respectively.Furthermore, a region indicated by ‘+’ represents a region having areflectance that is higher than a transmittance of light at the region,and a region indicated by dots ‘.’ represents a high reflection regionwhere a negative value of return loss due to reflection is greater thanor equal to 20 dB. A region indicated by oblique lines represents aregion of relatively high transmittance compared to other regions

In FIG. 3, interesting region is a region which is denoted as 310. Theregion 310 may include a very narrow region of relatively hightransmittance among a high reflectance region. The presence of the verynarrow region in the region 310 means that transmittance and reflectanceof light vary very sensitively to a change in wavelength in the region310 when a gap between the first and second reflective plates 110 and120 is determined. In other words, a linewidth of light of the region310 is very narrow because in the region 310, a transmittance of lightis rapidly changed even when there is a little change in a wavelength.

In FIG. 3, the simulation was performed when the first and secondreflective plates 110 and 120 are formed of silicon (Si). However, thefirst and second reflective plates 110 and 120 may be made of othervarious materials. In order to increase reflectance of light on thefirst and second reflective plates 110 and 120 as described above, thefirst and second reflective plates 110 and 120 may contain a materialhaving a refractive index higher than 3, but are not limited thereto.For example, each of the first and second reflective plates 110 and 120may include gallium phosphide (GaP), mercury sulfide (HgS), galliumarsenide (GaAs), germanium (Ge), Si, silicon dioxide (SiO₂), siliconnitride (SiN), indium phosphide (InP), or any combination thereof, butis not limited thereto.

A wavelength of light transmitted through the second reflective plate120 may be determined according to various variables. The wavelength oflight transmitted through the second reflective plate 120 may bedetermined by at least one selected from a thickness t of the first andsecond reflective plates 110 and 120, a refractive index of a materialof the first and second reflective plates 110 and 120, a distance dbetween the first and second reflective plates 110 and 120, sizes of thefirst and second holes 112 and 122, a spacing P1 between adjacent onesof the first holes 112, and a spacing P2 between adjacent ones of thesecond holes 122.

Among the above-described variables, the spacings P1 and P2 can beeasily adjusted during a process of manufacturing the optical filter 10.Thus, by adjusting the spacings P1 and P2, it may be possible to easilychange a wavelength to be filtered.

If the first and second holes 112 and 122 are not formed in the firstand second reflective plates 110 and 120, respectively, a Febry-Perotinterferometer model may be applied. In this case, a wavelength passingthrough the pixel 100 may be represented as a function of materials ofthe first and second reflective plates 110 and 120 and the distance dtherebetween. For more precise calculation, other variables describedabove have also to be considered.

However, according to the present embodiment, by forming the first andsecond holes 112 and 122 in the first and second reflective plates 110and 120, respectively, an effective value for the distance d substitutedfor applying a Febry-Perot model varies. In detail, when the first andsecond holes 112 and 122 are formed therein, a wavelength to be filteredis not determined based on a conventional Fabry-Perot model. Thus, tocorrect such an effect caused by the presence of the first and secondholes 112 and 122 during application of the conventional Fabry-Perotmodel, the distance d needs to be corrected as an effective value. Theeffective value may be traced quantitatively based on various computersimulations or experimental results.

An effective value for the distance d may be determined by sizes andshapes of the first and second holes 112 and 113 and the spacings P1 andP2. Thus, by manipulating these variables, a wavelength being filteredmay be easily changed.

FIG. 4 illustrates a simulation result showing a change in a wavelengthto be filtered according to spacings P1 and P2 between adjacent ones ofthe first holes 112 and between adjacent ones of the second holes 122 inthe optical filter 10 of FIG. 1.

The simulation result of FIG. 4 is obtained from a simulation performedusing RCWA. In the simulation, the first and second reflective plates110 and 120 were made of Si, and a thickness t of the first and secondreflective plates 110 and 120 was 265 nm, and a distance d between thefirst and second reflective plates 110 and 120 was 1.02 μm. To simplifycalculations, the first and second holes 112 and 122 had the same shapeas a slit and were arranged in the same repeating pattern. A fillingfactor, which is represented as a ratio (percentage) of an area of thefirst or second holes 112 or 122 to an area of a unit pattern, was setto 0.64 (64%). The unit pattern may mean the smallest unit of arepeating pattern in which the first and second holes 112 and 122 arearranged, as described in more detail below. Furthermore, the spacingsP1 and P2 were set to the same spacing value P.

FIG. 4 illustrates a graph of reflectance against a wavelength of lightincident on the pixel 100 of the optical filter 10 when the spacingvalue P of the spacings P1 and P2 are set to be 1.200 μm, 1.206 μm, and1.212 μm, respectively. A region with reflectance close to 1 is awavelength region where most light is reflected. A wavelength at thelowest point where reflectance is near 0 may be considered to be arepresentative value of a wavelength being transmitted through the pixel100 of the optical filter 10. As apparent from FIG. 4, when the spacingvalue P increases by only 0.006 μm (0.5%), a wavelength at a bottom peakwith the lowest reflectance value may be shifted to a larger value byapproximately 3 to 4 nm. In other words, if the spacing value Pincreases or decreases by only about 1%, a representative value of awavelength being transmitted through the pixel 100 may be shifted to alarger or smaller value by about 7 nm. Thus, by even slightly adjustingthe spacings P1 and P2 during a manufacturing process, it is possible toeasily change a wavelength being filtered.

Constructions of the optical filter 10 and the pixel 100 included in theoptical filter 10, and effects thereof have been described above withreference to FIGS. 1 through 4. Formation of a plurality of first holes110 and a plurality of second holes 120 in the first and secondreflective plates 110 and 120, respectively, according to embodimentswill now be described in greater detail.

FIG. 5 is a plan view of a plurality of the first (or second) holes 112(122) formed in the first (or second) reflective plate 110 (120) in theoptical filter 10 of FIG. 1.

As shown in FIG. 5, the slit-shaped first holes 112 are linearlyarranged in the first reflective plate 110. In this case, a wavelengthof light being filtered may vary according to a change in a width h ofeach of the first holes 112 and a spacing P between adjacent ones of thefirst holes 112. While FIG. 5 shows that the first holes 112 have thesame shape, they are not limited thereto. For example, each of the firstholes 112 may have a slit shape with a variation or have a trapezoidalshape. The spacing value P may also not be uniform. The same descriptionas presented with respect to FIG. 5 may also be applied to the secondreflective plate 120.

FIG. 6 illustrates a cross-section of the pixel 100 including the firstand second reflective plates 110 and 120 in the optical filter of FIG.1.

As shown in FIG. 6, the first and second holes 110 and 120 are formed inthe first and second reflective plates 110 and 120, respectively. Thefirst holes 112 are vertically aligned with the second hole 122. Forexample, each of the first holes 112 faces a corresponding one of thesecond holes 122, and they are not arranged in a staggered form. In theexample, if a distance d between the first and second reflective plates110 and 120 is decreased to 0, the first and second holes 112 and 122may overlap each other substantially. In this case, the first and secondholes 112 and 122 with the same shape may be arranged in the samepattern.

FIG. 7 illustrates another example of a cross-section of the pixel 100of FIG. 1.

As shown in FIG. 7, first and second holes 112 and 122 may be disposedin a staggered form rather than being aligned in a straight line. Thatis, if a distance d between the first and second reflective plates 110and 120 is decreased to 0, the first and second holes 112 and 122 maynot overlap each other completely.

FIG. 8 illustrates a plurality of first (or second) holes 112 (122)formed in the first (or second) reflective plate 110 (120) in theoptical filter 10 of FIG. 1, according to another exemplary embodiment.

As shown in FIG. 8, the plurality of first holes 112 are arranged in thefirst reflective plate 110 in a predetermined pattern. The predeterminedpattern may be a pattern in which a plurality of sub-regions, includinga sub-region 114, are repeatedly arranged in a two-dimensional (2D) way.Each of the plurality of sub-regions may include at least one first hole112, and be the smallest unit of a repeating pattern in which the firstholes are arranged. Each of the first and second reflective plates 110and 120 may include the plurality of sub-regions. The plurality ofsub-regions in the first reflective plate 110 may have the same shape asor a different shape from those in the second reflective plate 120.Furthermore, although a surface of the sub-region 114 has a trapezoidalshape, this is an example only, and the surface of the sub-region 114may have a polygonal shape or other 2D shapes. The above descriptionswith respect to FIG. 8 may be applied to both the first and secondreflective plates 110 and 120.

Although it has been described that the first and second holes 112 and122 are slit-shaped, exemplary embodiments are not limited thereto. Thefirst and second holes 112 and 122 may have a polygonal shape, acircular shape, or other 2D shapes in a plan view.

FIG. 9 illustrates a plurality of first (or second) holes, including afirst (or a second) hole 112 (122), which are formed in the first (orsecond) reflective plate 110 (120) of the optical filter 10 of FIG. 1,according to another exemplary embodiment.

As shown in FIG. 9, each of the plurality of first holes may becircular. The plurality of first holes are grouped into regularhexagonal sub-regions, including a sub-region 114, and the regularhexagonal sub-regions may be arranged in a 2D repeating pattern.However, exemplary embodiments are not limited thereto, and thesub-region 114 or the first hole 112 may have a different shape thanthat described above. The same descriptions as presented above withrespect to FIG. 9 may also be applied to the second reflective plate120.

FIGS. 5, 8, and 9 illustrate shapes and arrangements of the first andsecond holes 112 and 122 according to various exemplary embodiments. Asdescribed above, the first and second holes 112 and 122 may have variousshapes and sizes. When sizes of the first and second holes 122 change, apercentage of an area (or a filling factor) occupied by the first orsecond holes 112 or 122 within the sub-region 114 may vary. A wavelengthof light being filtered may be changed by adjusting a filling factor.Thus, to change a wavelength of light being filtered during a process ofmanufacturing the optical filter 10, the size of the first or secondholes 112 or 122 may be adjusted.

The optical filter 10 including at least one pixel 100 having the firstand second reflective plates 110 and 120 has been described above indetail. Components of the optical filter 10 other than those describedabove will now be described in detail.

The pixel 100 of the optical filter 10 may selectively transmit lightincident on the first reflective plate 110 according to a wavelength. Ingeneral, an angle at which light is incident on the first reflectiveplate 110 may not be uniform. Even when an incident angle is notuniform, the pixel 100 may perform a filtering function. However, iflight is incident on the first reflective plate 110 at various angles, awavelength region of the light being filtered may be different from anexpected value. To prevent such an error and more uniformly maintain afiltering performance of the pixel 100, an angle at which light isincident on the first reflective plate 110 needs to be adjusted.

FIG. 10 is a perspective view of an optical filter 10 according toanother exemplary embodiment.

As shown in FIG. 10, the optical filter 10 may further include a lens 12that changes a path of light incident on a first reflective plate 110.The lens 12 may be a convex lens, a concave lens, or a combinationthereof. The lens 12 may also change a path of light for all or onlysome of the pixels in the optical filter 10.

An optical measuring device employing the optical filter 10 according tothe exemplary embodiments will now be described in detail with referenceto FIG. 11.

The optical measuring device refers to a device capable of measuringintensity of incident light for each wavelength by analyzing a spectrumof the incident light. In a broad sense, the optical measuring devicemay include a system capable of analyzing a spectrum of light andinforming an analysis result to a user via various types of displays.The optical measuring device may also transmit a measurement result toanother device as simple data without displaying the measurement result.

FIG. 11 is an exploded perspective view of an optical measuring device1100 including an optical filter 10, according to another exemplaryembodiment. As shown in FIG. 11, the optical measuring device includesan optical filter 10 for selectively transmitting a predeterminedwavelength of incident light and a sensor 20 for measuring intensity ofthe light of the predetermined wavelength transmitted through theoptical filter 10. The optical filter 10 may include a plurality offirst pixels, including a first pixel 100, and the sensor 20 may includea plurality of second pixels, including a second pixel 200 correspondingto the first pixel 100. In this case, the optical filter 10 and thefirst pixel 100 may be the optical filter 10 and the first pixel 100described above with reference to FIGS. 1 through 10.

As described above, the first pixel 100 receives incident light andincludes a first reflective plate 110 having a plurality of first holes112 formed therein and a second reflective plate 120 that opposes and isseparated from the first reflective plate 110 by a predetermineddistance and has a plurality of second holes 122 formed therein.Although a distance between the optical filter 10 and the sensor 20looks relatively large, this is only for better visualization, and thusthe distance may be smaller or larger than that if necessary.

All the optical filters 10 according to the exemplary embodimentsdescribed with reference to FIGS. 1 through 10 may be used as theoptical filter 10 shown in FIG. 11. Thus, a wavelength of light beingtransmitted through the second reflective plate 120 may be determined byat least one selected from a thickness t of the first and secondreflective plates 110 and 120, a refractive index of a material of thefirst and second reflective plates 110 and 120, a distance d between thefirst and second reflective plates 110 and 120, sizes of the first andsecond holes 112 and 122, a spacing P1 between adjacent ones of thefirst holes 112, and a spacing P2 between adjacent ones of the secondholes 122.

Furthermore, the first and second holes 112 and 122 may be arranged in aregular pattern. The first holes 112 may have the same shape andarrangement pattern as the second holes 122. The first and second holes112 and 122 may have a slit shape or circular shape.

Each of the first and second reflective plates 110 and 120 may contain amaterial having a refractive index greater than 3. For example, each ofthe first and second reflective plates 110 and 120 may include GaP, HgS,GaAs, Ge, Si, SiO₂, SiN, InP, or any combination thereof. The opticalfilter 10 may further include a lens 12 for changing a path of lightincident on the first reflective plate 110.

Each of the plurality of second pixels, including the second pixel 200,receives light transmitted through a corresponding one of the firstpixels 100 to measure intensity of the light. To do so, each of theplurality of second pixels may include an optical sensor 210 formeasuring intensity of the light transmitted through the plurality offirst pixels, including the first pixel 100. The optical sensor 210 maybe a complementary metal-oxide-semiconductor (CMOS) image sensor (CIS)using a charge coupled device (CCD) or CMOS. Alternatively, the opticalsensor 210 may be a photodiode sensor for converting light energy intoelectrical energy.

The optical measuring device 1100 may provide a user with informationabout intensity of light measured by the plurality of second pixels,including the second pixel 200. Before providing such information to theuser, the optical measuring device 1100 may correct data measured by theplurality of second pixels. The optical measuring device 1100 mayfurther include a correction processor 30 for performing correction ofthe measured data. The correction processor 30 may be a hardware devicecapable of performing general calculations. Transmittance of lightthrough the plurality of first pixels, including the first pixel 100,may be considered when performing the correction. The need for thecorrection increases when the optical filter 10 includes the pluralityof first pixels and transmittance of light through each of the pluralityof first pixels 100 varies. Thus, the correction processor 30 in theoptical measuring device 1100 may correct data measured by each of theplurality of second pixels according to transmittance of light through acorresponding one of the plurality of first pixels. To achieve this, thecorrection processor 30 may include a memory for storing transmittanceof light through each of the plurality of first pixels.

In the optical filter 10 and the optical measuring device 1100 employingthe optical filter 10 according to the exemplary embodiments, theplurality of first holes 112 and the plurality of second holes 122 areformed in the first and second reflective plates 110 and 120,respectively. Such construction may increase reflectance of the firstand second reflective plates 110 and 120, thus decreasing a linewidth oflight. Furthermore, by adjusting the shape and size of the first andsecond holes 112 and 122 and spacings between adjacent first or secondholes 110 or 120, a wavelength of light being filtered may be easilychanged.

In the optical measuring device 1100 employing the optical filter 10,each of the plurality of first pixels, including the first pixel 100,selectively transmits a particular wavelength of light. In turn, each ofthe plurality of second pixels, including the second pixel 200, measuresintensity of the light transmitted from corresponding one of theplurality of first pixels. Thus, a separate space may not be requiredfor performing spectroscopy in order to analyze a spectrum of light, anda space for filtering of light may also be utilized efficiently. Theoptical measuring device 1100 may be used in cameras, contaminantdetection devices, biological analysis device, etc. As the size of theoptical measuring device 1100 decreases, it may also be applied tohealthcare-related devices. Thus, the optical measuring device 1100 maybe used in portable or wearable devices to measure biologicalinformation of a human body in a non-invasive and periodical way.

According to the exemplary embodiments, a linewidth of light may bereduced by forming a plurality of first holes and a plurality of secondholes in first and second reflective plates of an optical filter,respectively. Furthermore, it is possible to easily change a wavelengthbeing filtered by adjusting the shape and size of the first and secondholes and spacings between adjacent first or second holes.

In an optical measuring device employing an optical filter according toexemplary embodiments, each of pixels in the optical filter mayselectively transmit only light of a particular wavelength, and each ofpixels in a sensor may measure intensity of the transmitted light. Thus,the optical measuring device may not require a separate space forperforming spectroscopy in order to analyze a spectrum of light and mayefficiently utilize a space for filtering of light. The opticalmeasuring device may be used in cameras, contaminant detection devices,biological analysis equipment, etc. As the size of the optical measuringdevice decreases, it may also be applied to healthcare-related devices.Thus, the optical measuring device 1100 may be used in portable orwearable devices to measure biological information of a human body in anon-invasive and periodical way.

While one or more exemplary embodiments have been described withreference to the figures, it should be understood that the exemplaryembodiments described herein should be considered in a descriptive senseonly and not for purposes of limitation. The scope of the inventiveconcept is defined not by the detailed description provided above butinstead by the following claims.

What is claimed is:
 1. An optical filter comprising: a plurality ofpixels arranged next to one another, each of the plurality of pixelscomprising: a first reflective plate that is configured to receive lightand has first holes formed therein; and a second reflective plate thatfaces the first reflective plate, is separated from the first reflectiveplate by an air gap, and has second holes formed therein, the secondholes corresponding to the first holes in shape and orientation, thesecond reflective plate being configured to transmit the light of awavelength or the light of a range of wavelengths that has beentransmitted through the first reflective plate and is incident on thesecond reflective plate, wherein the light of the wavelength or thelight of the range of wavelengths is transmitted according to a spacingbetween adjacent holes of the first holes or a spacing between adjacentholes of the second holes, wherein at least one pixel, among theplurality of pixels, has the spacing between adjacent holes of the firstholes different from that of at least one other pixel, among theplurality of pixels, or has the spacing between adjacent holes of thesecond holes different from that of the at least one other pixel,wherein the first reflective plate is included in a plurality of firstreflective plates of the plurality of pixels, the plurality of firstreflective plates being arranged along a first plane, and wherein thesecond reflective plate is included in a plurality of second reflectiveplates of the plurality of pixels, the plurality of second reflectiveplates being arranged along a second plane parallel to the first plane.2. The optical filter of claim 1, wherein the wavelength or the range ofwavelengths of the light transmitted through the second reflective platecorresponds to a thickness of the first reflective plate and the secondreflective plate, respectively.
 3. The optical filter of claim 1,wherein the wavelength or the range of wavelengths of the lighttransmitted through the second reflective plate corresponds to arefractive index of a material of the first reflective plate and thesecond reflective plate, respectively.
 4. The optical filter of claim 1,wherein the wavelength or the range of wavelengths of the lighttransmitted through the second reflective plate corresponds to adistance between the first reflective plate and the second reflectiveplate.
 5. The optical filter of claim 1, wherein the wavelength or therange of wavelengths of the light transmitted through the secondreflective plate corresponds to sizes of the first and second holes. 6.The optical filter of claim 1, wherein the first holes and the secondholes have a same arrangement pattern.
 7. The optical filter of claim 6,wherein the first holes are vertically aligned to overlap with thesecond holes.
 8. The optical filter of claim 1, wherein the first andsecond holes have a slit shape or a circular shape.
 9. The opticalfilter of claim 1, wherein at least two of the plurality of pixelstransmit light of different wavelengths.
 10. The optical filter of claim1, further comprising a lens configured to change a path of the lightreceived by the first reflective plate.
 11. The optical filter of claim1, wherein each of the first reflective plate and the second reflectiveplate comprises a material having a refractive index greater than
 3. 12.The optical filter of claim 1, wherein each of the first reflectiveplate and the second reflective plate comprises at least one selectedfrom a group consisting of gallium phosphide (GaP), mercury sulfide(HgS), gallium arsenide (GaAs), germanium (Ge), silicon (Si), silicondioxide (SiO₂), silicon nitride (SiN), indium phosphide (InP), and anycombinations thereof.
 13. The optical filter of claim 1, wherein each ofthe first reflective plate and the second reflective plate is arectangular plate which has a thickness less than a distance between thefirst reflective plate and the second reflective plate, the distancecorresponding to the air gap.
 14. An optical measuring device comprises:an optical filter comprising a plurality of first pixels arranged nextto one another, each of the plurality of first pixels comprising: afirst reflective plate configured to receive light and having firstholes formed therein, and a second reflective plate that faces the firstreflective plate, is separated from the first reflective plate by an airgap, and has second holes formed therein, the second reflective platebeing configured to transmit the light of a wavelength or the light of arange of wavelengths that has been transmitted through the firstreflective plate and is incident on the second reflective plate, thesecond holes corresponding to the first holes in shape and orientation;and a sensor that is configured to measure an intensity of lighttransmitted through the optical filter and includes a plurality ofsecond pixels, each of the plurality of second pixels corresponding toeach of the plurality of first pixels in a one to one relationship andbeing configured to measure the intensity of light transmitted through acorresponding first pixel, wherein the light of the wavelength or thelight of the range of wavelengths is transmitted according to a spacingbetween adjacent holes of the first holes or a spacing between adjacentholes of the second holes, wherein at least one first pixel, among theplurality of first pixels, has the spacing between adjacent holes of thefirst holes different from that of at least one other first pixel, amongthe plurality of first pixels, or has the spacing between adjacent holesof the second holes different from that of the at least one other firstpixel, wherein the first reflective plate is included in a plurality offirst reflective plates of the plurality of first pixels, the pluralityof first reflective plates being arranged along a first plane, andwherein the second reflective plate is included in a plurality of secondreflective plates of the plurality of first pixels, the plurality ofsecond reflective plates being arranged along a second plane parallel tothe first plane.
 15. The optical measuring device of claim 14, whereinthe wavelength or the range of wavelengths of the light transmittedthrough the second reflective plate corresponds to at least one selectedfrom a thickness of the first reflective plate and the second reflectiveplate, respectively, a refractive index of a material of the firstreflective plate and the second reflective plate, a distance between thefirst reflective plate and the second reflective plate, and sizes of thefirst and second holes.
 16. The optical measuring device of claim 15,further comprising a correction processor configured to receive theintensity of light measured in at least one second pixel among theplurality of second pixels, and correct the intensity of light measuredin the at least one second pixel in consideration of transmittance oflight transmitted through the corresponding first pixel.
 17. The opticalmeasuring device of claim 14, wherein the first holes and the secondholes have a same arrangement pattern.
 18. The optical measuring deviceof claim 14, wherein the first and second holes have a slit shape orcircular shape.
 19. The optical measuring device of claim 18, whereinthe optical filter further comprises a lens configured to change a pathof the light received by the first reflective plate.
 20. The opticalmeasuring device of claim 18, wherein each of the first reflective plateand the second reflective plate comprises a material having a refractiveindex greater than
 3. 21. The optical measuring device of claim 18,wherein each of the first reflective plate and the second reflectiveplate comprises at least one selected from a group consisting of galliumphosphide (GaP), mercury sulfide (HgS), gallium arsenide (GaAs),germanium (Ge), silicon (Si), silicon dioxide (SiO₂), silicon nitride(SiN), indium phosphide (InP), and any combinations thereof.
 22. Theoptical measuring device of claim 18, wherein each of the plurality ofsecond pixels comprises an optical sensor configured to measure theintensity of light transmitted through the corresponding first pixel.